The present invention relates to wood-stump processing machines for reducing wood-stumps into a plurality of pieces by pressing them through a grid comprising a plurality of cutting plates. The reduced pieces may then be subjected to further processing, as for example, to produce wood mulch, or firewood.
In densely populated urban areas, one problem which land developers face when clearing wooded areas is to dispose of the tree stumps. A common practice at present is to collect and transport the stumps to a waste dump or land fill area. However, because the cost of land in most urban areas is so high, the use of a large amount of land as a temporary waste dump or permanent land fill necessarily results in excessive costs for stump disposal. Some appreciation of the cost involved may be gained from knowing that it is not uncommon in a large urban area to have to dispose of hundreds of truck loads of stumps each day at a cost of hundreds of dollars per truck load. The consequent high cost of disposal of the wood-stumps, i.e. transportation, labor, and equipment presents a severe economic burden. Of course, the alternative of burning the stumps is not practical because of the detrimental effects on the environment; similarly, burying the stumps is usually banned because the decay of the stumps tends to generate harmful methane gas which may adversely affect the ground water.
There is, therefore, a need for a more economical and environmentally acceptable solution to present day wood-stump disposal practices. The present invention provides such a solution since it accomplishes the effective and rapid processing, at low cost, of the wood-stumps while at the same time producing a useful by-product, thereby eliminating the adverse environmental factors. This is accomplished according to the present invention by providing a massive tree stump processing machine into which a large quantity of stumps may be placed at the same time, together with a means for pressing the stumps through a cutting grid so as to cut the stumps into a plurality of relatively small pieces which may thereafter be further reduced into still smaller pieces to generate, for example, wood mulch or firewood. Also, since the process carried out necessarily results in extreme compression of the cut pieces of wood, water and also tree sap are squeezed out of the resulting pieces, thereby resulting not only in a drier, lighter product but also providing with the collected tree sap a useful by-product.
The reducing of tree stumps presents problems which are quite different from the mere slicing of logs. Thus, the various wood-stumps are of highly irregular shape and size, and the direction of the grain of the wood within each stump is quite irregular. It is also essential to be able to process various types and sizes of wood-stumps simultaneously in a single batch. Moreover, the wood-stumps when being processed in the equipment are in their natural state, as they are collected from the land, not cleaned, debarked, or prepared in any way. It is also not feasible to orient or reposition the stumps which are loaded into the apparatus for the purpose of aligning the grain with direction of movement through the cutting grid, not only because of the labor involved in doing so but also because of the irregular nature of the grain in a stump as previously mentioned. It is of course apparent that a machine which is intended to press a number of tree stumps through a cutting grid must be constructed to have enormous strength, and this is particularly true of the cutting grid itself. The apertured cutting grid must be provided on each of its peripheral edges with a cutting edge; but clearly, considering the forces which must of necessity be applied by such cutting edges, they cannot be of razor-like thinness. Typically, the minimum width of the cutting edge is in the order of one-quarter of an inch. Such a cutting edge must of necessity be able to resist extremely large forces in the stump cutting operation, and this means that the cutting edge must be supported on a member of great strength and correspondingly large thickness, typically in the order of 3 inches, and with a depth in the direction of stump movement of about 24 inches.
It follows from these requirements that the aperture must define an opening that is significantly smaller in area that the area circumscribed by the cutting edges surrounding any aperture in the grid, and the consequence of this is that the section of the stump that is extrude through each aperture necessarily becomes considerably compressed in its cross-section. In turn, a consequence of this compression is that the stump section that is forced through each section of the grid tends to be tightly wedged within the aperture; therefore, at the conclusion of each extrusion operation, there is a tendency for a number of the stump sections to clog the cutting grid and extend at varying lengths below the grid, thereby making it difficult, and at times impossible, for the comminuted stump sections below the grid to be removed since the presence of the underhanging sections interferes with the operation of removal equipment, such as a railed cart for example. It is accordingly an important feature of the invention that the means which forces the stump through the cutting grid has the capability of completely forcing each of the individual stump sections entirely through the apertures in the grid.
Wood processing machines for press splitting wood logs into individual pieces are known in the art, for example from U.S. Pat. No. 4,478,203 or Canadian Pat. No. 1,097,197. Both patents however relate to machines and processes for splitting a single log into a plurality of individual pieces by pressing the log through a cutting grid. The log is first debarked and precut to a specific (length) thickness. The splitting is then performed in such a manner that it occurs substantially along the grain of the wood. This necessarily requires that each log be oriented in such a way in the equipment that the cutting can occur along the length of the grain; this is clearly not practical for reducing tree stumps for reasons described above.
In log splitting machines known in the prior art, each log loaded into the splitting chamber pushes the previous log through the grid apertures to complete extrusion of the wood pieces from the cutting grid apertures. Such prior art wood processing machines are not suitable for processing of a plurality of wood-stumps of differing wood species and sizes as also described above. Therefore, the problems which must be solved in a method and apparatus for cutting/splitting of wood-stumps present different tasks than the compression-splitting of wood-logs.